1. Field of the Invention
This invention relates to an air conditioning apparatus having a first air passage and a second air passage, formed in an air conditioning case, in which inside air and outside air are introduced into the first air passage and the second air passage, respectively.
2. Description of Related Art
In a conventional air conditioning apparatus as disclosed in JP-A-5-124426, there are formed at one end side of an air conditioning case an inside-air inlet for introducing inside air and an outside-air inlet for introducing outside air and at the other end side of the air conditioning case a foot air outlet for blowing air toward a foot area, a defroster air outlet for blowing air toward an inner surface of a windshield, and a face air outlet for blowing air toward a face area.
In the air conditioning case, there is provided a partition plate for partitioning an interior of the air conditioning case into a first air passage extending from the outside-air suction port to the face air outlet and the foot air outlet and a second air passage extending from the outside-air suction port to the defroster air outlet.
Further, in each of the first and the second air passages, there are provided a cooling evaporator, a heating heat exchanger, a bypass passage bypassing the heating heat exchanger, and an air mixing door.
When any one of the face mode, the bi-level mode, and the foot mode is selected as air outlet mode, if the inside air/outside air introduction mode is set to the inside-air introduction mode, the inside air is introduced into both air passages, whereas if the mode is set to the outside-air introduction mode, the outside air is introduced into both air passages.
Further, the foot mode is selected as the air outlet mode, the inside air/outside air double laminar mode in which the inside air is introduced into the first air passage and the outside air is introduced into the second air passage is set. In this way, because a passenger compartment is heated by a recirculation of the inside air which has been already heated, the heating performance is improved. Further, because the outside air having a low humidity is blown toward the windshield, it is possible to obtain the defrosting performance of the windshield certainly.
The inventors of the present invention have experimentally produced the air conditioning apparatus having a function of the above-described inside air/outside air double laminar mode, and studied the control for preventing the frosting of the cooling evaporator. As a result, it turns out that the following problem occurs.
That is, in the air conditioning apparatus for a vehicle, as being known well, an operation of the compressor for generating a circulation of the refrigerant is intermitted according to the cooling temperature of the cooling evaporator (more specifically the temperature of the air just blown out from the evaporator) to maintain the cooling temperature of the cooling evaporator at a set temperature (e.g., 3° C.–4° C.). In this way, the frosting of the cooling evaporator is prevented.
Here, as shown in FIGS. 11A and 11B in a case where a temperature sensor 39 for detecting the cooling temperature of the cooling evaporator 7 (more specifically the temperature of the blown-air) is disposed in the inside-air passage (the first air passage) 13, in summer season where the outside-air temperature is high, the temperature of air blown from the cooling evaporator 7 in the outside-air passage (the second air passage) 14 is higher than that in the inside-air passage 13, as shown in FIG. 11A, because the high-temperature outside air flows into the outside-air passage 14.
On the other hand, in winter season where the outside-air temperature is low, as shown in FIG. 11B, the temperature of air blown from the cooling evaporator 7 in the outside-air passage (the second air passage) 14 is lower than that in the inside-air passage 13, because the low-temperature outside air flows into the outside-air passage 14. Accordingly, in winter season, the cooling temperature of the cooling evaporator 7 is lowered to be less than 0° C. so that the evaporator may be frosted.
When the temperature sensor 39 is disposed in the outside-air passage 14 as shown in FIGS. 11C and 11D, in summer season when the outside temperature is high, the temperature of the air blown from the cooling evaporator 7 in the inside-air passage 13 is lower than that in the inside-air passage 14, as shown in FIG. 11C, because the low-temperature inside air flows into the inside-air passage 13. Therefore, in order to prevent the frosting of the cooling evaporator 7 in the inside-air passage 13 certainly, a set temperature of the temperature sensor 39 needs to be higher than the cases shown in FIGS. 11A and 11B by 5° C.–6° C. for example.
However, if the set temperature of the temperature sensor 39 is set to be higher as described above, in winter season where the outside-air temperature is low, the temperature of the blown-air in the inside-air passage 13 is increased by 10° C. for example as shown in FIG. 1D, there occurs a problem that the dehumidifying capacity for the inside-air is insufficient.
In view of the above-described problem, an object of the present invention is to prevent the frosting of the cooling heat exchanger in winter season certainly, which is mounted on the air conditioning apparatus for a vehicle, having a first air passage and a second air passage, formed in an air conditioning case, in which inside air and outside air are introduced into the first air passage and the second air passage, respectively.
Further, another object of the present invention is to solve the insufficiency of the dehumidifying capacity for the inside air in winter season.